1. Field of the Invention
The present invention relates to an explosive booster for initiating a propagative explosion in a low-energy explosive connecting cord, e.g., for transmitting a detonation from a donor detonating cord to a receiver low-energy detonating cord; and to an assembly containing said booster in combination with a trunkline and a downline for initiating an explosive charge in a borehole.
2. Description of the Prior Art
Explosive connecting cords are used in non-electric blasting systems to convey or conduct an initiating impulse, i.e., a detonation or deflagration pressure wave, to an explosive charge in a borehole from a remote area. One type of connecting cord used to transmit a detonation impulse is low-energy detonating cord (LEDC), which can be used as a trunkline and/or a downline cord to transmit the impulse to a non-electric blasting cap positioned in the charge in the hole.
One type of LEDC which has recently been developed is described in U.S. Pat. No. 4,232,606. This cord has, enclosed within a plastic sheath, a continuous solid core of a deformable bonded detonating explosive composition comprising a crystalline high explosive compound, e.g., superfine pentaerythritol tetranitrate (PETN), admixed with a binding agent, the crystalline high explosive loading being about from 0.1 to 2 grams per meter of length. Another type of LEDC, described in U.S. Pat. No. 3,125,024, has a core of granular PETN having a specific surface of 900-3400 cm.sup.2 /g confined within a woven textile sheath surrounded by a protective covering such as a thermoplastic layer. In addition, a currently available explosive connecting cord which propagates a shock or percussion wave consists of a plastic tube coated on the inside with a thin layer of an explosive substance such as PETN, RDX, or HMX powder (U.S. Pat. No. 3,590,739).
In blasting practice, lengths of explosive connecting cords must be joined to other lengths of the same or different cords, e.g., in the joining of downlines to a trunkline, and the explosion must be transmitted from one cord to the other. Depending on its structure and composition, a low-energy receiver cord may or may not be able to "pick up", i.e., to detonate or deflagrate as the case may be, from the detonation of a donor cord with which it is spliced or knotted.
U.S Pat. No. 4,248,152, issued Feb. 3, 1981, describes an explosive booster adapted to be used with LEDC to permit the latter to reliably initiate, or be initiated by, another detonating cord. This booster contains a granular explosive charge, e.g., PETN, between the walls and closed bottoms of inner and outer shells, one cord being held in an axial cavity in the inner shell in a manner such that an end-portion of the cord is surrounded by the booster explosive, and another cord being positioned transversely outside and adjacent the closed end of the outer shell. One of the cords (donor) initiates the booster explosive and this in turn initiates the other cord (receiver), which usually is LEDC. Cord-gripping means for holding the cord in the inner shell's cavity is shown. The booster is capable of transmitting a detonation from a trunkline to a single downline.